For years, wireless communications have struggled with limitations of audio/video/data transport and internet connectivity in both obstructed (indoor/outdoor) and line-of-site (LOS) deployments.
A focus on antenna gain as well as circuitry solutions have proven to have significant limitations. Unresolved, non-optimized (leading edge) technologies have often given way to “bleeding edge” attempted resolutions. Unfortunately, all have fallen short of desirable goals, and some ventures/companies have even gone out of business as a result.
While lower frequency radio waves benefit from an ‘earth hugging’ propagation advantage, higher frequencies do inherently benefit from (multi-) reflection/penetrating characteristics. However, with topographical changes (hills & valleys) and object obstructions (e.g., natural such as trees, and man-made such as buildings/walls) and with the resultant reflections, diffractions, refractions and scattering, maximum signal received may well be off-axis (non-direct path) and multi-path (partial) cancellation of signals results in null/weaker spots. Also, some antennas may benefit from having gain at one elevation angle (‘capturing’ signals of some pathways), while other antennas have greater gain at another elevation angle, each type being insufficient where the other does well. In addition, the radio wave can experience altered polarizations as they propagate, reflect, refract, diffract, and scatter. A very preferred (polarization) path may exist, however, insufficient capture of the signal can result if this preferred path is not utilized.
Spatial diversity can distinctly help with some of the null-spot issues. Some radio equipment comes equipped with two switched antenna connections to reduce null spot problems experienced by a single antenna due to multi-path signals. A single antenna may receive signals out of phase from different paths, causing the resultant received signal to be nulled out (i.e., the individual signals received from the different paths cancel each other out). With two antennas, if one antenna is experiencing null cancellation, the other, if positioned properly with respect to the first antenna, will not. VOFDM (Vector Orthogonal Frequency Division Multiplexing) technology helps with some multi-path out-of-phase ‘data clash’ issues. Electronically steer-able antenna arrays alleviate some interference problems and provide a solution where multiple standard directional antenna/radio systems would otherwise be more difficult or clearly impractical. Dual slant polarization antenna/circuitry switching systems have shown much advantage over others in (some) obstructed environments but require additional complex circuitry. Circularly polarized systems can also provide some penetration advantages.
Certainly, gain (increased ability to transmit and receive signals in a particular direction) is important. However, if polarization of the signal and antenna are not matched, poor performance may likely result. For example, if the transmitting antenna is vertically polarized and the receiving antenna is also vertically polarized, then the transmitting and receiving antennas are matched for wireless communications. This is also true for horizontally polarized transmitting and receiving antennas.
However, if a first antenna is horizontally polarized (e.g., a TV house antenna) and a second antenna (e.g., TV transmitting antenna) is vertically polarized, then the signal received by the first antenna will be reduced, due to polarization mismatch, by about 20 dB (to about 1/100th of the signal that could be received if polarizations were matched). For example, a vertically polarized antenna with 21 dBi of gain, attempting to receive a nearly horizontally polarized signal, is essentially a 1 dBi gain antenna with respect to the horizontally polarized signal and may not be effective.
As another example, a vertically or horizontally polarized antenna that is tilted at 45 degrees can receive both vertically and horizontally polarized signals, but at a power loss of 3 dB (½ power). However, if the signal to be received is also at a 45-degree tilt, but perpendicular to the 45-degree tilt of the receiving antenna, then the signal is again reduced to 1/100th of the potential received signal. Having two antennas where one is vertically polarized and the other is horizontally polarized can help, but still has its disadvantages. Therefore, gain is important but, to be effective, polarization should be considered as well.
Traditional beam antennas such as, for example, the Yagi-Uda antenna, the quad-beam antenna, and the quagi antenna, provide higher gain substantially in one direction. Beam antennas are often desirable where transmission and reception along primarily one direction is desired such as, for example, communication between two spatially separated towers, or between a tower and customer premise equipment (CPE).
The Yagi-Uda and quagi antennas use a reflector element positioned behind a driven element, and director elements positioned in front of the driven element. All of the elements are co-linear (i.e., positioned along an imaginary line in space). A focused beam of electromagnetic energy is formed in the far field along the co-linear direction. However, such antennas tend to suffer from a poor ability to receive signals of many different polarizations and have limited spatial diversity.
Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.